Compound (I) to be used in the present invention is reported as an inhibitor of dipeptidyl peptidase (DPP-IV), which is an enzyme that decomposes glucagon-like peptide-1 (GLP-1), which is a hormone enhancing insulin secretion (patent reference 1).
However, a preparation comprising compound (I) or a salt thereof and pioglitazone or a salt thereof has not been reported.    [patent reference 1] US-B-2005/0261271